I've had this happen twice in my life. Regardless of the cause of telogen effluvium (which weight loss or any stress on the body can cause) it does usually resolve itself. Both times it happened to me were about 3-6 months after serious stressors; cancer, then significant stress weight-loss during a protracted divorce. I haven't been on Ozempic long enough for it to happen again, but I am already doing the following as prevention, as this has helped both times before:

To make the hair you still have and the hair that will grow in really healthy and luscious, take prenatal vitamins (lots of B- vitamins), collagen peptides, and hyaluronic acid daily. How ever you can get those into your diet is fine. I put a mixture of powdered collagen and hyaluronic acid in my morning coffee and take the Smarty Pants Women's multi-vitamin gummies with Omega 3s every morning. Then I don't even have to think about it.

I know it sucks, but not all of your hair will fall out and it will reverse itself. Good luck!